Solve for $q$ : $-20 = q - 7$
Add $7$ to both sides: $ \begin{eqnarray} \\ \hphantom{-20 {+ 7}} &\hphantom{=}& \hphantom{q} \\ -20 &=& q - 7 \\ \\ {+7} && {+7} \\ \end{eqnarray} $ $ \begin{eqnarray} \\ -20 {+ 7} &=& q \\ \end{eqnarray} $ Simplify. $ q = -13$